1. Field of the Invention
The present invention relates, in general, to gaseous fuel injection systems for motor vehicles.
2. State of the Art
Over the past several years, the automotive industry has shifted from the use of carburetors to electronic fuel injection to improve emissions and drivability in gasoline powered vehicles. These gasoline powered fuel injection systems are of two basic types: throttle body injection and port injection. In a throttle body fuel injection system, one or more injectors are mounted above the throttle plates attached to the intake manifold of the engine. Fuel is injected by the injectors at precise rates and mixed with air in the throttle body and intake manifold to provide the desired air/fuel ratio for all cylinders. In a port injection system, an injector is mounted at each cylinder port and injects fuel directly into the cylinder port where it is mixed with air to form the desired air/fuel mixture.
Currently, there is new interest in using alternate fuels to meet governmental emission requirements and fuel economy standards and to reduce dependence on foreign oil. Alternate fuels being investigated for potential use in automotive vehicles are natural gas and liquid petroleum gas which can be stored in tanks mounted on the vehicle. Heretofore, such gaseous powered vehicles use a gas supply ring to supply gas just above a disabled conventional gasoline carburetor or employ a special gaseous fuel carburetor. Injection of gaseous fuel into the vehicle engine ports or via throttle body injection has also been proposed. The injection of gaseous fuel into a throttle body at the cylinder port is sensitive to variations in manifold pressure, gas temperature and gas pressure caused by engine operating and environmental conditions. Such variations require extensive control techniques in order to maintain the desired quantity of injected fuel over the wide range of engine operating conditions.
One unique approach to overcome variations in fuel flow due to variations in manifold pressure is to inject gaseous fuel at sonic flow rates. In this way, the amount of fuel injected is proportional to injection valve open time and is independent of manifold pressure. However, this approach generates unacceptable high noise levels since the injectors are mounted above the throttle body and are surrounded only by the air cleaner. Thus, it would be desirable to provide a gaseous fuel injection system which provides sonic flow rate injection of the fuel at acceptable low noise levels.
Another problem encountered in the use of gaseous fuels in vehicle engines is the dependency of fuel flow rates on gas temperature and pressure. Prior art gaseous fuel engines utilize a number of sensors and other control devices to monitor the gas temperature and pressure, to maintain the gas temperature and pressure at desirable levels and to control air/fuel ratios based on variations in gas temperature and pressure. Such sensors and additional control devices add to the cost of the gaseous fuel system and make control of the quantity of injected gaseous fuel into the engine much more difficult. Thus, it would be desirable to provide a gaseous fuel system which eliminates the need for gas temperature and gas pressure sensors and other control devices.
Finally, the use of gaseous fuels in automotive vehicles creates problems in the placement of the tanks used to store the gases under high pressure. The high tank pressure required allows little flexibility in storage tank shape. Heretofore, such tanks have been placed in the bed of a pickup truck or inside the passenger compartment of a van. This consumes needed cargo and passenger space and necessarily limits the number of tanks which can be conveniently mounted on a vehicle. It is usually desirable to provide multiple tanks on a single vehicle to provide an adequate operating range between fill-ups. Thus, it would be desirable to provide a unique gaseous fuel tank mounting arrangement which enables multiple tanks to be conveniently and safely mounted on a vehicle without consuming needed cargo or passenger space.